Typically, a data storage device such as a magnetic disc drive, an optical storage device, and a removable disc drive, among others, contains a medium or data storage surface on which data is stored by writing to the media using a transducer, or head. Similarly, data is retrieved from the media by using the head in a read mode. The transducer is normally positioned a specific distance from the media, commonly referred to as a head-disc gap. A spindle motor and a voice coil motor are able to change the relative position of the head and media by a positioning control means. A read/write channel allows communication between the head, positioning control means, and a controller. The controller's main functions are to receive and interpret commands from an outside source, usually an interface adapter on a computer system bus, and transmit control signals to the read/write channel and positioning control means.
A data storage surface, as used in a typical hard disc drive, is commonly divided into multiple data zones oriented in the radial direction. Each data zone typically comprises a set of tracks. Typically, data is stored on the tracks in sectors. Tracks in the outer data zones are longer than those in the inner data zones, thus the tracks in the outer data zones are able to store more data than the tracks in the inner data zones. In this configuration, the additional capacity in the outer data zones is utilized by having a larger number of sectors on each track in the outer data zones. This results in the number of data sectors per track varying from zone to zone.
With the use of hard disc drives, the concept of “flying” heads is generally adopted and can be similarly applied to other data storage devices having similar reading and writing mechanisms. The flying effect of a head is usually achieved by the special design of the air-bearing surface on the head structure that generates elevation whenever there is a difference in air pressure on the head caused by the spinning of the data storage surface. As the rotational speed of the data storage surface increases, so does the head-disc gap created by this phenomenon. At the point when the target rotational speed is reached, a controlled head-disc gap is created that enables the head to glide across the data storage surface effortlessly without actual contact with the data storage surface.
Any head that is flying too low to the data storage surface will incur at least two major risks. First, probability of flight disturbances will be high due to the presence of uneven micro-bumps on the data storage surface. This will often cause “skipped writes” and other read/write abnormalities. A skipped write is an abnormal write event where the writer/head experiences a sudden lift away from the disc surface. This is normally caused by a disturbance in the air flow or particle contact. This event is thought to be caused at times by the inherent lack of spacing between head and the disc where the probability of air disturbance or particle contact is higher. The final result of such an event is a badly written region which leads to user errors. Second, there is a higher risk of head to surface contact. This can result in smearing, scratching, or even a head crash.
All of these effects are often aggravated by changes in the device temperature. Any temperature increase will cause a corresponding change in air pressure, which may affect the head-disc gap and in turn will cause the head to fly lower. Any such effects are undesirable and may cause long-term reliability issues.
Historically, previous methods have measured head-disc gap by a number of different techniques. The previous methods have also tried to estimate the short-term effect of flight disturbances on the data storage device's operation.
However, there are problems with the previous methods. The previous methods do not predict long-term drive failure. Also, many of the previous methods require the addition of special hardware to the data storage device, thus increasing the cost and complexity of the device. Typically, the previous methods used servo data to perform calculations. This method can not be used to predict long term device reliability issues because servo data is usually recorded at a lower recording frequency than user data. This is due to the fact that the analysis of data recorded at a lower frequency results in less sensitive and accurate measurement of critical effects on a data storage device. Furthermore, the effect of flight disturbances on user data is ultimately what is important to the user, not the effect on servo data.
Even further, the previous methods do not effectively predict data storage device failure due to individual problem areas, collectively problematic regions of the data storage surface, problematic heads, or data storage surfaces in general. Also, the previous methods neglect the effect of varying data density on recording signal strength. Increased data density improves the storage capacity of the device, but can result in data interfering with neighboring data. This phenomenon is known in the art as Inter-Symbol Interference (ISI). Along with head-disc spacing, inter-symbol interference can also affect signal strength. Thus, fly-height abnormalities at an area of higher data density on the data storage surface will have a greater effect on signal strength than fly-height abnormalities at an area of lower data density.
The present invention provides a solution to these and other problems, and offers other advantages over the prior art.